This invention relates generally to apparatus or machine which place a tensioned loop about an article. The invention is particularly directed to the manner in which the strap is guided through the passageway or strap channel of such apparatus.
In typical strap feed and tension mechanisms of known strapping apparatus or machines, strap from a supply is engaged by two or more wheels, at least one of which is positively driven, as by a reversible motor, to effect strap advancement and retraction. With such mechanisms, motion is transmitted to the strap simply by nipping the strap between rolls, or by the traction exerted on the strap by substantial portions of the rolls' surfaces, or by both nipping the strap and exerting traction along significant lengths thereof. U.S. Pat. No. Re.27,744 describes a strap feed and tension mechanism or strap drive assembly which is illustrative of those employed in conventional strapping machines.
Many prior art strapping machines secure the opposing overlapped ends by welding or heat sealing them. This is accomplished by inserting a hot heat seal blade between the ends until the plastic becomes molten on the opposing surfaces. The blade is then withdrawn and the overlapped ends pressed together until the plastic solidifies thereby sealing the ends together.
Although the performance of modern strapping apparatus has shown constant improvement, they are still not entirely satisfactory. Apparatus which use plastic strap still have abrasion problems caused by the strap impacting the various components of the apparatus as it passes through the strap passageway. The strap is also caused to abrade in those cases where it is driven by rollers operating at different speeds. Such abraded strap may be weakened by having its molecular orientation disturbed, its surface marred to such an extent as to make subsequent use of the strap difficult, and by creating dust particles which may interfere with the strap's passage through the machine, either by blocking the passage or to cause portions of the machine to malfunction.
Some of these problems have been recognized. For example, the problem with abraded strap in a particular feed and tension mechanism by U.S. Pat. No. 4,328,742, issued to J. L. Discavage. This patent teaches a feed and tension mechanism actuated by a reversible drive mechanism. The feed and tension mechanism is of the type having two wheels of equal diameter, one of which is driven, for feeding and tensioning the strap. Abrasion of the strap is minimized by placing meshing gears as flanges on the two wheels, which act as guides and which rotate with the wheels. Accordingly, the two wheels rotate at the same speed.
Another problem with prior art machines is that the region of the seal is less than optimum in that the ends of the straps are sometimes skewed, i.e. not parallel to one another. This results in a reduced seal area and hence reduced strength. Additionally, the ends occasionally are not fully overlapped thus also reducing the seal area and the strength of the seal. In some cases the strap ends are in such undesirable positions before the heat seal blade is used and in other cases properly aligned strap ends are missaligned by the insertion of the blade, or more commonly, by its withdrawal.
Abrasion and jams tend to occur in strapping apparatus at various points along the strap passage. One such point is between the strap drive assembly and the forward guide, and between the forward guide and the forward gripper, as well as within the forward guide itself. Another problem with prior art strapping apparatus is that some of those which are adapted to use straps of different widths have removable guides therefore. Not only is the extra guide an additional expense, but time is required to change the guides.
Some front guides located between the drive mechanism and seal mechanism, of the prior art, have been laterally adjustable through the use of shims so as to obtain the proper clearance between the strap and guide. However, such guides have had only one side thereof adjustable with respect to the body of the guide. Not only has this been time consuming, but it has resulted in the shifting of the strap from the passage centerline, when the prior art guide was adjusted. Additionally, prior art guides have had to be removed for cleaning, a time consuming and, therefore, costly step.